The present application relates to a semiconductor structure and a method of forming the same. More particularly, the present application relates to a semiconductor structure containing at least a first metal resistor structure having a first nitrogen content and a second metal resistor structure having a second nitrogen content that differs from the first nitrogen content, and a method of forming such a semiconductor structure.
A resistor is one of the most common electrical components, and is used in almost every electrical device. In semiconductor device fabrication, it is well known to have thin film resistors embedded in the back-end-of-line (BEOL) structures of the chip through either a damascene approach or a subtractive etch method. BEOL thin film resistors are generally preferred over other types of resistors because of the lower parasitic capacitance. Conventional resistor materials and fabrication methods, however, present a number of challenges.
In one approach, the sheet resistivity of various resistors formed over an entire wafer may vary and go beyond specifications due to poor process control. In an advanced manufacturing line, wafers out of specification are often scrapped for quality control, which is expensive.
One material used for resistors is doped polysilicon. A problem with this conventional resistor material is that it can only provide a limited resistance within a limited dimension, which presents problems as further miniaturization of the device features continues. Resistive thin films such as chromium silicide (CrSi) and tantalum nitride (TaN) are also used as resistors in semiconductor devices. Prior art metal nitride resistors such as TaN are generally formed by physical vapor deposition and as such the nitrogen content within such resistors is less than 50 atomic percent. Manufacturing metal nitride resistors having a nitrogen content that is greater than 50 atomic percent, %, nitrogen is not possible using prior art deposition techniques due to nitrogen poison related problems which are inherently present in such deposition processes.